Tin or tin alloy plating solution

ABSTRACT

A tin or tin alloy plating solution includes: (A) a soluble salt containing at least a stannous salt; (B) an acid selected from an organic acid and an inorganic acid or a salt thereof; (C) a surfactant; and (D) a leveling agent. In addition, the surfactant contains polyoxyethylene polyoxypropylene alkylamine, an alkyl group of the polyoxyethylene polyoxypropylene alkylamine is C a H2 a+1  (where a is 12 to 18). Further, in a case where a number of a functional group of polyoxypropylene of the polyoxyethylene polyoxypropylene alkylamine is set as p and a number of a functional group of polyoxyethylene of the polyoxyethylene polyoxypropylene alkylamine is set as q, the sum of p and q (p+q) is 8 to 21, and a ratio of p to q (p/q) is 0.1 to 1.6.

TECHNICAL FIELD

The present invention relates to a plating solution of tin or a tinalloy plating solution for producing a bump serving as a bump electrodeof tin or a tin alloy on a substrate in a case of mounting asemiconductor integrated circuit chip on a circuit board. The inventionmore particularly relates to a tin or tin alloy plating solution havingexcellent via filling properties for vias on a substrate even in apattern having different bump diameters, and a uniform height of formedbumps.

Priority is claimed on Japanese Patent Application No. 2017-205201,filed on Oct. 24, 2017 and Japanese Patent Application No. 2018-197081,filed on Oct. 19, 2018, the contents of which are incorporated herein byreference.

BACKGROUND ART

In a circuit board on which a semiconductor integrated circuit chip(hereinafter, referred to as a semiconductor chip) is to be mounted, achip size/scale package (CSP) type semiconductor device having a packagesubstrate area that is reduced to approximately the same size as that ofa semiconductor chip to be mounted on the substrate is currently mainlyproduced, in order to respond to light and thin products. In order toconnect the circuit board and the semiconductor chip to each other, avia opening which is a via body on a substrate side is filled with tinor a tin alloy to form a bump which is a bump electrode of a protrudingmetal terminal, and this bump is s loaded with a semiconductor chip.

In the related art, in a case of forming a bump by the filling of thetin or tin alloy material, the via body is filled with a conductivepaste such as a tin-based solder paste or a tin-based solder ball, or atin-plated deposition layer is formed in the via by an electroplatingmethod using a plating solution of tin or a tin alloy, and then, theconductive paste, the solder ball, or the tin-plated deposition layer ismelted by a heat treatment.

A general method for forming a bump by the electroplating method will bedescribed with reference to FIG. 1. As shown in FIG. 1(a), a solderresist pattern having an opening is formed on a surface of a substrate 1on which wirings and the like are provided. Next, electroless plating isperformed on a surface of the solder resist layer 2 to form a copperseed layer 3 for power supply. Next, a dry film resist layer 4 is formedon a surface of the copper seed layer 3, and a dry film resist patternhaving an opening is formed so as to be connected to the opening of thesolder resist layer 2. Next, by supplying power through the copper seedlayer 3, electric tin plating is performed in a via 6 of the dry filmresist pattern, and a tin plating deposition layer 7 (tin plating film)is formed in the via 6 on the copper seed layer 3. Next, after the dryfilm resist layer and the copper seed layer are sequentially removed,the remaining tin plating deposition layer is melted by a reflowprocess, and a tin bump 8 is formed as shown in FIG. 1(b).

Previously, in a case of forming a tin or tin alloy bump using theelectroplating method, the improvement regarding via filling propertiesof vias on the substrate or prevention of empty spaces in the bump hasbeen made by changing the content components of the tin or tin alloyplating solution (for example, see PTLs 1, 2, 3, and 4).

PTL 1 discloses a tin or tin alloy plating solution containing acompound of specific α,β-unsaturated aldehyde or specificα,β-unsaturated ketone. PTL 1 discloses that this plating solution has ahigh via-fill effect, and in a case where this plating solution is used,tin plating is selectively deposited in a recessed portion, therebyobtaining a tin plating deposit having substantially no empty spaces,and no burning or abnormal precipitation occurs on the formed tinplating film surface, thereby obtaining a tin plating film havingpractical and good appearance with excellent solderability or colorfastness.

PTL 2 discloses a tin or tin alloy plating solution including (a) acarboxyl group-containing compound, and (b) a carbonyl group-containingcompound, in which a content of the component (a) is 1.3 g/L or more,and a content of the component (b) is 0.3 g/L or more. PTL 2 disclosesthat this plating solution can be filled in a blind via or a throughhole with high reliability in a short period of time by electroplating aplating object having a blind via or a through hole, and can be used inthree-dimensional mounting of a semiconductor, a filling step in a blindvia or a through hole in a printed wiring board, or formation of siliconthrough electrode.

PTL 3 discloses a tin or tin alloy plating solution containing inorganicacid, organic acid, and a water-soluble salt thereof, a surfactant, anda leveling agent. Here, the surfactant is at least one nonionicsurfactant selected from the group consisting of polyoxyalkylene phenylether or a salt thereof, and polyoxyalkylene polycyclic phenyl ether ora salt thereof, the phenyl constituting polyoxyalkylene phenyl ether,and polycyclic phenyl constituting the polyoxyalkylene polycyclic phenylether may be substituted with an alkyl group having 1 to 24 carbon atomsor a hydroxy group, and the leveling agent may be at least one selectedfrom the group consisting of an aliphatic aldehyde, an aromaticaldehyde, an aliphatic ketone, and an aromatic ketone; andα,β-unsaturated carboxylic acid or an amide thereof, or a salt thereof.PTL 3 discloses that, by containing a specific nonionic surfactant andtwo specific leveling agents, it is possible to have excellent recessedportion filling properties (via filling properties) and to preventgeneration of empty spaces. Accordingly, in a case of using this platingsolution, it is possible to provide a good bump which is smooth withouta recessed portion and without the generation of empty spaces afterreflow.

Further, PTL 4 discloses a tin alloy electroplating solution for formingbump electrodes, containing (A) a soluble salt consisting of any of astannous salt and a mixture of a stannous salt and a salt of a metalselected from silver, copper, bismuth, nickel, indium, and gold, (B) anacid or a salt thereof, and (C) a filling organic compound selected fromthe group consisting of an aromatic and aliphatic aldehyde, an aromaticand aliphatic ketone, unsaturated carboxylic acids, and aromaticcarboxylic acids, and (D) a nonionic surfactant. PTL 4 discloses that,since a combination of the specific compound (C) which prevents theprecipitation of a tin-based material and the component (D) is used inthis plating solution, it is possible to effectively prevent theprecipitation on an upper portion of a via, cause the precipitation ofthe tin-based material to preferentially proceed towards the upper sideof the via from ma bottom portion of the via, and smoothly fill the viawhile preventing the generation of empty spaces, thereby forming a bumpelectrode in an excellent manner after reflow or without reflow andobtaining excellent brazing bonding strength electrical properties.

CITATION LIST Patent Literature

[PTL 1] Japanese Unexamined Patent Application, First Publication No.2014-125662 (Claim 2, paragraph [0020])

[PTL 2] Japanese Unexamined Patent Application, First Publication No.2015-007276 (Claim 1, paragraphs [0011] and [0012])

[PTL 3] Japanese Unexamined Patent Application, First Publication No.2015-193916 (Claim 1, paragraph [0019])

[PTL 4] Japanese Unexamined Patent Application, First Publication No.2016-074963 (Claim 1, paragraph [0019])

DISCLOSURE OF INVENTION Technical Problem

In recent years, wiring patterns having different bump diameters or bumppitches have been mixed on one circuit board. In such complicated wiringpatterns, it is necessary to form all bumps at a uniform height, even ina case where the bump diameters and the bump pitches are different.According to the tin or tin alloy plating solutions of PTLs 1 to 4, thegeneration of empty spaces in the bumps is prevented, the via on thesubstrate can be filled with high reliability in a short period of time,and the via filling properties and appearance are excellent. However,the plating solutions for substrates in PTLs do not aim at achievingbump height uniformity.

Specifically, as shown in FIG. 2, in the case of a pattern havingdifferent bump diameters, in a case of performing plating using a tin ortin alloy plating solution of the related art, it is possible to improvethe via filling properties of either a via having a small diameter or avia having a large diameter, while the via filling properties of theother one are deteriorated. That is, in a case of performing the platingon both vias at the same time on a substrate having both vias having asmall diameter and a large diameter, it is difficult to perform theplating on both vias with excellent via filling properties. As describedabove, in a case where vias having different via filling properties arepresent (FIG. 2(b)), a dispersion in height of the bumps after thereflow increases, and it is difficult to achieve bump height uniformity(FIG. 2(d)). Therefore, in order to achieve the bump height uniformity(FIG. 2(c)), as shown in FIG. 2(a), it is necessary to improve viafilling properties for both vias having a small diameter and a largediameter.

An object of the invention is to provide a tin or tin alloy platingsolution which having excellent via filling properties for vias on asubstrate even in a pattern having different bump diameters, and auniform height of formed bumps.

Solution to Problem

According to a first viewpoint of the present invention, there isprovided a tin or tin alloy plating solution including: (A) a solublesalt containing at least a stannous salt; (B) an acid selected from anorganic acid and an inorganic acid or a salt thereof; (C) a surfactant;and (D) a leveling agent, in which the surfactant containspolyoxyethylene polyoxypropylene alkylamine, an alkyl group of thepolyoxyethylene polyoxypropylene alkylamine is C_(a)H_(2a+1) (where a is12 to 18), in a case where a number of a functional group ofpolyoxypropylene of the polyoxyethylene polyoxypropylene alkylamine isset as p and a number of a functional group of polyoxyethylene of thepolyoxyethylene polyoxypropylene alkylamine is set as q, the sum of pand q (p+q) is 8 to 21, and a ratio of p to q (p/q) is 0.1 to 1.6.

In a second viewpoint of the present invention, there is provided thetin or tin alloy plating solution according to the first viewpoint,further including: two or more of a surfactant other than thesurfactant, an antioxidant, and an alcohol having 1 to 3 carbon atoms.

According to a third viewpoint of the present invention, there isprovided a method for forming a bump by forming a tin or tin alloyplating deposition layer on a substrate using the tin or tin alloyplating solution according to the first or second viewpoint, and then byperforming a reflow process.

According to a fourth viewpoint of the invention, there is provided amethod for producing a circuit board using a bump formed by the methodaccording to the third viewpoint.

Advantageous Effects of Invention

In the tin or tin alloy plating solution of the first viewpoint of theinvention, a specific amine structure in which the surfactant containspolyoxyethylene polyoxypropylene alkylamine, an alkyl group of thepolyoxyethylene polyoxypropylene alkylamine is C_(a)H_(2a+1) (where a is12 to 18), in a case where a number of a functional group ofpolyoxypropylene of the polyoxyethylene polyoxypropylene alkylamine isset as p and a number of a functional group of polyoxyethylene of thepolyoxyethylene polyoxypropylene alkylamine is set as q, the sum of pand q (p+q) is 8 to 21, and a ratio of p to q (p/q) is 0.1 to 1.6 isprovided, and accordingly, it is possible to perform the plating on asurface to be plated by preventing the precipitation of Sn ions duringplating. In particular, according to this plating solution, in the caseof a pattern having different bump diameters, polarization resistance isgreat, even in a case where the bump diameter is large or small, andaccordingly, the via filling properties for vias on a substrate areexcellent, and a height of formed bumps become uniform.

The tin or tin alloy plating solution according to the second viewpointof the invention further includes two or more of a surfactant other thanthe surfactant containing polyoxyethylene polyoxypropylene alkylamine,an antioxidant, and an alcohol having 1 to 3 carbon atoms, andaccordingly the following effects are exhibited. The surfactant otherthan the surfactant containing polyoxyethylene polyoxypropylenealkylamine exhibits effects such as stabilization of the platingsolution, improvement of solubility, and the like. In addition, theantioxidant prevents the oxidation of a soluble stannous salt to a tindioxide salt. Further, the alcohol exhibits an effect of improvingsolubility of the surfactant.

In the method for forming a bump according to the third viewpoint of theinvention, a bump is formed by forming a tin or tin plating depositionlayer on a substrate using the tin or tin alloy plating solution, andthen by performing a reflow process, and accordingly, it is possible toform bumps having a uniform height, even with a pattern having differentbump diameters.

In the method for producing a circuit board according to the fourthviewpoint of the invention, a circuit board is produced using a bumpformed by the method according to the third viewpoint, and accordingly,it is possible to produce a semiconductor device having high reliabilitywithout electrical connection failure.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1(a) is a cross-sectional configuration diagram in which a platingdeposition layer is formed in a via of the invention, and FIG. 1(b) is across-section configuration diagram after peeling off a dry film and acopper seed layer and heating the plating deposition layer.

FIG. 2(a) is a cross-sectional configuration diagram showing an examplein which a plating deposition layer is formed uniformly in a patternhaving different bump diameters (via diameters), FIG. 2(b) is across-sectional configuration diagram showing an example in which aplating deposition layer is formed non-uniformly in a pattern havingdifferent bump diameters (via diameters), FIG. 2(c) is a cross-sectionalconfiguration diagram showing an example in which a height of formedbump becomes uniform, after peeling off a dry film and a copper seedlayer and heating the plating deposition layer in FIG. 2(a), and FIG.2(d) is a cross-sectional configuration diagram showing an example inwhich the height of formed bump varies, after peeling off a dry film anda copper seed layer and heating the plating deposition layer in FIG.2(b).

BEST MODE FOR CARRYING OUT THE INVENTION

Next, an embodiment for carrying out the invention will be described.

The tin or tin alloy plating solution of the invention includes (A) asoluble salt containing at least a stannous salt, (B) an acid selectedfrom an organic acid and an inorganic acid or a salt thereof, (C) asurfactant, and (D) a leveling agent. The surfactant containspolyoxyethylene polyoxypropylene alkylamine.

The soluble salt consists of any of a stannous salt and a mixture of astannous salt and a salt of a metal selected from silver, copper,bismuth, nickel, antimony, indium, and zinc.

The tin alloy of the invention is an alloy of tin and a predeterminedmetal selected from silver, copper, bismuth, nickel, antimony, indium,and zinc, and examples thereof include a tin-silver alloy, a tin-copperalloy, a tin-bismuth alloy, a tin-nickel alloy, a tin-antimony alloy, atin-indium alloy, a binary alloy of a tin-zinc alloy, and a ternaryalloy such as a tin-copper-bismuth alloy or tin-copper-silver alloy.

Therefore, the soluble salt (A) of the invention means any soluble saltthat generates various metal ions such as Sn²⁺, Ag⁺, Cu⁺, Cu²⁺, Bi³⁺,Ni²⁺, Sb³⁺, In³⁺, and Zn²⁺ in the plating solution, and examples thereofinclude an oxide and a halide of the metal, and the metal salt ofinorganic acid or organic acid.

Examples of metal oxide include a stannous oxide, a copper oxide, anickel oxide, a bismuth oxide, an antimony oxide, an indium oxide, and azinc oxide. Examples of the halide of metal include a stannous chloride,a bismuth chloride, a bismuth bromide, a cuprous chloride, a cupricchloride, a nickel chloride, an antimony chloride, an indium chloride,and a zinc chloride.

Examples of the metal salt of inorganic acid or organic acid includecopper sulfate, stannous sulfate, bismuth sulfate, nickel sulfate,antimony sulfate, bismuth nitrate, silver nitrate, a copper nitrate,antimony nitrate, indium nitrate, nickel nitrate, zinc nitrate, copperacetate, nickel acetate, nickel carbonate, sodium stannate, stannousborofluoride, stannous methanesulfonate, silver methanesulfonate, coppermethanesulfonate, bismuth methanesulfonate, nickel methanesulfonate,indium methanesulfonate, zinc bismethanesulfonate, stannousethanesulfonate, and bismuth 2-hydroxypropanesulfonate.

The acid or a salt thereof (B) of the invention is selected from organicacid, inorganic acid, or a salt thereof. Examples of the organic acidinclude organic sulfonic acid such as alkanesulfonic acid,alkanolsulfonic acid, and aromatic sulfonic acid, and aliphaticcarboxylic acid. Examples of the inorganic acid include borofluoricacid, Hydrofluorosilicic acid, sulfamine acid, hydrochloric acid,sulfuric acid, nitric acid, and perchloric acid. Examples of the saltthereof include a salt of alkali metal, a salt of alkaline earth metal,an ammonium salt, an amine salt, and a sulfonate. The component (B) ispreferably organic sulfonic acid from a viewpoint of solubility of themetal salt or ease of wastewater treatment.

As the alkanesulfonic acid, a material represented by a chemical formulaG_(r)H_(2r+1)SO₃H (for example, r=1 to 5, preferably 1 to 3) can beused, and specific examples thereof include methanesulfonic acid,ethanesulfonic acid, 1-propanesulfonic acid, 2-propanesulfonic acid,1-butanesulfonic acid, 2-butanesulfonic acid, pentanesulfonic acid,hexanesulfonic acid, decanesulfonic acid, and dodecanesulfonic acid.

As the alkanolsulfonic acid, a material represented by a chemicalformula C_(s)H_(2s+1)—CH(OH)—C_(t)H_(2t)—SO₃H (for example, s=0 to 6,t=1 to 5) can be used, and specific examples thereof include2-hydroxyethane-1-sulfonic acid, 2-hydroxypropane-1-sulfonic acid,2-hydroxybutane-1-sulfonic acid, 2-hydroxypentane-1-sulfonic acid,1-hydroxypropane-2-sulfonic acid, 3-hydroxypropane-1-sulfonic acid,4-hydroxybutane-1-sulfonic acid, 2-hydroxyhexane-1-sulfonic acid,2-hydroxydecane-1-sulfonic acid, and 2-hydroxydodecane-1-sulfonic acid.

The aromatic sulfonic acid is basically benzene sulfonic acid, alkylbenzene sulfonic acid, phenol sulfonic acid, naphthalene sulfonic acid,or alkyl naphthalene sulfonic acid, and specific examples thereofinclude 1-naphthalene sulfonic acid, 2-naphthalene sulfonic acid,toluenesulfonic acid, xylenesulfonic acid, p-phenolsulfonic acid,cresolsulfonic acid, sulfosalicylic acid, nitrobenzenesulfonic acid,sulfobenzoic acid, and diphenylamine-4-sulfonic acid.

Examples of the aliphatic carboxylic acid include acetic acid, propionicacid, butyric acid, citric acid, tartaric acid, gluconic acid,sulfosuccinic acid, and trifluoroacetic acid.

The alkyl group of the polyoxyethylene polyoxypropylene alkylamine ofthe invention is C_(a)H_(2a+1) (where a is 12 to 18). In a case where anumber of a functional group of polyoxypropylene of the polyoxyethylenepolyoxypropylene alkylamine is set as p and a number of a functionalgroup of polyoxyethylene of the polyoxyethylene polyoxypropylenealkylamine is set as q, the sum of p and q (p+q) is 8 to 21, and a ratioof p to q (p/q) is 0.1 to 1.6. Specifically, the polyoxyethylenepolyoxypropylene alkylamine of the invention is represented by one ortwo or more formulae selected from the group consisting of GeneralFormulae (1) to (4). Here, not only one of General Formulae (1) to (4),but also two or more formulae are included because a plurality of aminesrepresented by General Formulae (1) to (4) may be mixed.

Here, in General Formulae (1) to (4), R¹ is C_(a)H_(2a+1) (a is 12 to18), p and q are each 1 or more, (p+q) is 8 to 21, and p/q is 0.1 to1.6. Here, in a case where a is less than 12, there is a problem thatthe via filling properties are deteriorated, and in a case where a ismore than 19, the polyoxyethylene polyoxypropylene alkylamine is hardlydissolved in the plating solution or abnormal appearance of the platingoccurs. In addition, in a case where (p+q) is less than 8, thepolyoxyethylene polyoxypropylene alkylamine is hardly dissolved in theplating solution, or abnormal appearance of the plating occurs. In acase where (p+q) is more than 21, the polyoxyethylene polyoxypropylenealkylamine is hardly dissolved in the plating solution, the via fillingproperties are deteriorated, and abnormal appearance of the platingoccurs. Further, in a case where p/q is less than 0.1, abnormalappearance of plating occurs, and in a case where p/q is greater than1.6, the polyoxyethylene polyoxypropylene alkylamine is hardly dissolvedin the plating solution, or abnormal appearance of the plating occurs.

The polyoxyethylene polyoxypropylene alkylamine is formed of analternating copolymer, a periodic copolymer, a block copolymer, or arandom polymer of polyoxyethylene (EO) and polyoxypropylene (PO).Examples of the molecular formulae of the alternating copolymer, theperiodic copolymer, and the block copolymer are shown in the Formulae(5) and (6), respectively. In this case, EO/PO ratio=(q+q)/(p+p)=q/p.R₁—N-(EO)_(q+q)-(PO)_(p+p)-H  (5)R¹—N-(PO)_(p+p)-(EO)_(q+q)-H  (6)

The leveling agent (D) of the invention is added to form a uniform anddense plating film and to smooth the plating film. In order to improvethe via filling properties and prevent the generation of empty spaces,two types of a first leveling agent (D-1) and a second leveling agent(D-2) are used. Examples of the first leveling agent (D-1) include oneor two or more selected from the group consisting of aliphatic aldehyde,aromatic aldehyde, aliphatic ketone, and aromatic ketone, and examplesof the second leveling agent (D-2) include α,β-unsaturated carboxylicacid or amide thereof, and salt thereof.

The first leveling agent (D-1) is a carbonyl compound containingaldehyde or ketone, and does not include α,β-unsaturated carboxylic acidof the second leveling agent (D-2). Specific examples are as follows.Examples of the aliphatic aldehyde include formaldehyde, acetaldehyde,and allyl aldehyde. Examples of the aromatic aldehyde includebenzaldehyde, 2-chlorobenzaldehyde, 3-chlorobenzaldehyde,4-chlorobenzaldehyde, 2,4-dichlorobenzaldehyde,2,6-dichlorobenzaldehyde, 2,4,6-trichlorobenzaldehyde, 1-naphthaldehyde,2-naphthaldehyde, 2-hydroxybenzaldehyde, 3-hydroxybenzaldehyde,4-hydroxybenzaldehyde, 2-methylbenzaldehyde, 3-methylbenzaldehyde,4-methylbenzaldehyde, m-anisaldehyde, o-anisaldehyde, andp-anisaldehyde. In addition, examples of the aliphatic ketone includeacetylacetone. Further, examples of the aromatic ketone includebenzylideneacetone (synonymous with benzalacetone),2-chloroacetophenone, 3-chloroacetophenone, 4-chloroacetophenone,2,4-dichloroacetophenone, and 2,4,6-trichloroacetophenone. These may beused alone or in combination of two or more types thereof. A preferredcontent of the first leveling agent (D-1) in an electroplating bath (anamount of a single substance, in a case where it is used alone, and atotal amount of substances, in a case where two or more types areincluded) is 0.001 g/L. to 0.3 g/L and more preferably 0.01 g/L to 0.25g/L. In a case where the content of the component is small, the effectof adding the component is not sufficient, and on the other hand, in acase where the content of the component is excessively large, thesmoothing of the plating film may be inhibited.

Examples of the second leveling agent (D-2) include acrylic acid,methacrylic acid, picolinic acid, crotonic acid, 3-chloroacrylic acid,3,3-dimethylacrylic acid, 2,3-dimethylacrylic acid, methyl acrylate,ethyl acrylate, n-butyl acrylate, isobutyl acrylate, 2-ethylhexylacrylate, ethyl methacrylate, n-butyl methacrylate, isobutylmethacrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate,2-dimethylaminoethyl methacrylate, methacrylic anhydride, and methylmethacrylic acid. In addition, the second leveling agent (D-2) alsoincludes amide of α,β-unsaturated carboxylic acid (for example,acrylamide or the like) and a salt of α,β-unsaturated carboxylic acid(for example, potassium, sodium, or ammonium). A preferred content ofthe second leveling agent (D-2) in an electroplating bath (an amount ofa single substance, in a case where it is used alone, and a total amountof substances, in a case where two or more types are included) is 0.01g/L. to 50 g/L, more preferably 0.05 g/L to 30 g/L, and even morepreferably 0.05 g/L to 10 g/L. In a case where the content of thecomponent is small, the effect of adding the component is notsufficient, and on the other hand, in a case where the content of thecomponent is excessively large, the smoothing of the plating film may beinhibited.

The tin or tin alloy plating solution of the invention preferablyfurther includes two or more of a surfactant (E) other than thesurfactant containing the polyoxyethylene polyoxypropylene alkylamine,an antioxidant (F), and alcohol (G) having 1 to 3 carbon atoms.

In this case, examples of the other surfactant (E) include an ordinaryanionic surfactant, a cationic surfactant, a nonionic surfactant, and anamphoteric surfactant.

Examples of the anionic surfactant include polyoxyalkylene alkyl ethersulfate such as sodium polyoxyethylene (ethylene oxide: containing 12mol) nonyl ether sulfate, polyoxyalkylene alkyl phenyl ether sulfatesuch as sodium polyoxyethylene (ethylene oxide: containing 12 mol)dodecylphenyl ether sulfate, alkyl benzene sulfonate such as sodiumdodecylbenzene sulfonate, naphthol sulfonate such as sodium1-naphthol-4-sulfonate or disodium 2-naphthol-3,6-disulfonate,(poly)alkylnaphthalenesulfonate such as sodiumdiisopropylnaphthalenesulfonate or sodium dibutylnaphthalenesulfonate,and alkyl sulfate such as sodium dodecyl sulfate or sodium oleylsulfate.

Examples of cationic surfactant include mono-trialkylamine salt,dimethyldialkylammonium salt, trimethylalkylammonium salt,dodecyltrimethylammonium salt, hexadecyltrimethylammonium salt,octadecyltrimethylammonium salt, dodecyldimethylammonium salt,octadecenyl dimethylethylammonium salt, dodecyldimethylbenzylammoniumsalt, hexadecyldimethylbenzylammonium salt,octadecyldimethylbenzylammonium salt, trimethylbenzylammonium salt,triethylbenzylammonium salt, hexadecylpyridinium salt, dodecylpyridiniumsalt, dodecylpicolinium salt, dodecylimidazo linium salt, oleylimidazolinium salt, octadecylamine acetate, and dodecylamine acetate.

Examples of the nonionic surfactant include a material obtained byadding and condensing 2 to 300 mol of ethylene oxide (EO) and/orpropylene oxide (PO) to sugar ester, fatty acid ester, C₁ to C₂₅ alkoxylphosphoric acid (salt), sorbitan ester, and C₁ to C₂₂ aliphatic amide,and sulfated or sulfonated adducts of the condensation products ofsilicon-based polyoxyethylene ether, silicon-based polyoxyethyleneester, fluorine-based polyoxyethylene ether, fluorine-basedpolyoxyethylene ester, ethylene oxide and/or propylene oxide andalkylamine or diamine.

Examples of the amphoteric surfactant include betaine, carboxybetaine,imidazolinium betaine, and sulfobetaine, aminocarboxylic acid.

The antioxidant (F) is used for preventing the oxidation of the solublestannous salt to the tin dioxide salt. Examples of antioxidant includehypophosphorous acids, ascorbic acid or a salt thereof, phenolsulfonicacid (Na), cresolsulfonic acid (Na), hydroquinonesulfonic acid (Na),hydroquinone, α- or β-naphthol, catechol, resorcin, phloroglucin,hydrazine, phenolsulfonic acid, catecholsulfonic acid,hydroxybenzenesulfonic acid, naphtholsulfonic acid, and salts thereof.

The alcohol (G) having 1 to 3 carbon atoms is used for improving thesolubility of the surfactant. Examples of the alcohol include methanol,ethanol, 1-propanol, and 2-propanol. The alcohol can be used alone or incombination of two or more kinds thereof.

A content of the surfactant (C) in the plating solution is 0.5 g/L to 50g/L and preferably 1 g/L to 5 g/L. In a case where the content is lessthan the lower limit, plating failure such as a dendrite occurs due toan excessive supply of Sn ions. In addition, in a case where the contentexceeds the upper limit, Sn ions hardly reach a surface to be plated,and the via filling properties may be deteriorated (decreased).

The predetermined soluble metal salt (A) can be used alone or incombination, and a content thereof in the plating solution is 30 g/L to100 g/L and preferably 40 g/L to 60 g/L. In a case where the content isless than the appropriate range, the productivity is reduced, and in acase where the content increases, the cost of the plating solutionincreases.

The organic acid and inorganic acid or a salt thereof (B) can be usedalone or in combination, and a content thereof in the plating solutionis 80 g/L to 300 g/L and preferably from 100 g/L to 200 g/L. In a casewhere the content is less than the appropriate range, electricalconductivity is low and a voltage increases, and in a case where thecontent increases, viscosity of the plating solution increases and astirring speed of the plating solution decreases.

Meanwhile, a temperature of the electroplating solution of the inventionis generally 70° C. or lower and preferably 10° C. to 40° C. A currentdensity during the formation of a plating film by electroplating is in arange of 0.1 A/dm² to 100 A/dm² and preferably in the range of 0.5 A/dm²to 20 A/dm². In a case where the current density is excessively low, theproductivity deteriorates, and in a case where the current density isexcessively high, the height uniformity of the bumps deteriorates.

By applying the plating solution of the tin or tin alloy containing thesurfactant (C) of the invention to a circuit board which is a materialto be plated, a predetermined metal film can be formed on the circuitboard. Examples of the circuit board include a printed circuit board, aflexible printed circuit board, and a semiconductor integrated circuitboard.

EXAMPLES

Next, examples of the invention will be described in detail togetherwith comparative examples.

Surfactant (C) Used in Examples and Comparative Examples

Tables 1 to 4 show each structural formula of polyoxyethylenepolyoxypropylene alkylamine which is the surfactant (C) used in Examples1 to 10 and Comparative Examples 1 to 6, and a structural formula ofpolyoxyethylene polyoxypropylene ethylenediamine which is the surfactant(C) used in Comparative Example 7. In addition, Table 5 shows values ofa, p, q, (p+q) and (p/q) in General Formula (1) or (2) of the surfactant(C).

The values of p, q, (p+q) and (p/q) are calculated by ¹H-NMR from asignal strength of ¹H of a C—H bond within the repetition of p and q. Inaddition, in the invention, the surfactant (C) may not be composed ofonly a single polyoxyethylene polyoxypropylene alkylamine, but maycontain a plurality of types of polyoxyethylene polyoxypropylenealkylamine. That is, for example, in the case of polyoxyethylenepolyoxypropylene alkylamine in which p=1 and q=10, polyoxyethylenepolyoxypropylene alkylamine in which p=2, q=9 or q=11 may be included.

TABLE 1 No. of compound of surfactant Structural formula of compound ofsurfactant C-1 (a = 14) (p = 1) (q = 10) (p/q = 0.10)

C-2 (a = 18) (p = 4) (q = 7) (p/q = 0.57)

C-3 (a = 12) (p = 4) (q = 4) (p/q = 0.90)

C-4 (a = 12) (p = 5) (q = 4) (p/q = 1.56)

TABLE 2 No. of compound of surfactant Structural formula of compound ofsurfactant C-5 (a = 18) (p = 2) (q = 8) (p/q = 0.13)

C-6 (a = 15) (p = 4) (q = 17) (p/q = 0.33)

C-7 (a = 12) (p = 5) (q = 15) (p/q = 0.35)

C-8 (a = 16) (p = 7) (q = 9) (p/q = 0.76)

C-9 (a = 13) (p = 8) (q = 6) (p/q = 1.51)

TABLE 3 No. of compound of surfactant Structural formula of compound ofsurfactant C-10 (a = 12) (p = 1) (q = 15) (p/q = 0.07)

C-11 (a = 15) (p = 13) (q = 7) (p/q = 1.92)

C-12 (a = 20) (p = 5) (q = 5) (p/q = 1.10)

C-13 (a = 10) (p = 4) (q = 10) (p/q = 0.51)

C-14 (a = 9) (p = 13) (q = 7) (p/q = 1.92)

TABLE 4 No. of compound of surfactant Structural formula of compound ofsurfactant C-15 (a = 12) (p = 6) (q = 16) (p/q = 0.38)

C-16 (a = 18) (p = 0) (q = 5) (p/q = 0.00)

C-17

TABLE 5 General Compound Formula No. applied a p q p + q p/q C-1 Formula(1) 14 1 10 11 0.10 C-2 Formula (3) 18 4 7 11 0.57 C-3 Formula (1) 12 44 8 0.90 C-4 Formula (1) 12 5 4 9 1.56 C-5 Formula (2) 18 2 8 10 0.13C-6 Formula (2) 15 4 17 21 0.33 C-7 Formula (2) 12 5 15 20 0.35 C-8Formula (4) 16 7 9 16 0.76 C-9 Formula (2) 13 8 6 14 1.51 C-10 Formula(1) 12 1 15 16 0.07 C-11 Formula (3) 15 13 7 20 1.92 C-12 Formula (1) 205 5 10 1.10 C-13 Formula (1) 10 4 10 14 0.51 C-14 Formula (1) 9 13 7 201.92 C-15 Formula (1) 12 6 16 22 0.38 C-16 Formula (1) 18 0 5 5 0.00C-17 — — — — — — Appropriate — 12 to 1≤ 1≤ 8 to 21 0.1 to range 18 1.6

Example 1 Preparation of Sn Plating Solution

Methanesulfonic acid as a free acid, hydroquinone as an antioxidant,1-naphthaldehyde as a first leveling agent, and methacrylic acid as asecond leveling agent were mixed with a Sn methanesulfonate aqueoussolution to form a uniform solution, and then, the polyoxyethylenepolyoxypropylene alkylamine (mass average molecular weight: 1,300) ofthe (C-1) was further added thereto as a surfactant. Ion-exchanged waterwas finally added to prepare a Sn plating solution having the followingcomposition. The Sn methanesulfonate aqueous solution was prepared byelectrolyzing a metal Sn plate in a methanesulfonic acid aqueoussolution.

Composition of Sn Plating Solution

Sn methanesulfonate (as Sn²⁺): 50 g/L

Potassium methanesulfonate (as free acid): 100 g/L

Surfactant (C-1): 2 g/L

Hydroquinone (as the antioxidant (F)): 1 g/L

1-naphthaldehyde (as the first leveling agent (D-1)): 0.1 g/L

Methacrylic acid (as the second leveling agent (D-2)): 2 g/L

Ion-exchanged water: balance

Examples 2 to 10 and Comparative Examples 1 to 7

In Examples 2 to 10 and Comparative Examples 1 to 7, polyoxyethylenepolyoxypropylene alkylamine ((C-2) to (C-16)) of the structural formulaeshown in Tables 1 to 4 were used as the surfactant (C). Except this, Snplating solutions of Examples 2 to 10 and Comparative Examples 1 to 7were prepared in the same manner as in Example 1. In Example 4 andComparative Example 4, Ag was included as metal other than Sn (1.0 g/Las Ag⁺), and in Example 6 and Comparative Example 1, Cu was included asmetal other than Sn (0.5 g/L as Cu²⁺).

Comparative Example 8

In Comparative Example 8, polyoxyethylenepolyoxypropylene-ethylenediamine (C-17) of the structural formula shownin Table 4 was used as the surfactant (C). Except for this, a Sn platingsolution of Comparative Example 8 was prepared in the same manner as inExample 1. In Comparative Example 8, Ag was included as metal other thanSn (1.0 g/L as Ag⁺).

Comparative Test 1 and Evaluation

The plating was performed on a substrate having a pattern havingdifferent bump diameters using the 18 types of the prepared platingsolutions of Examples 1 to 10 and Comparative Examples 1 to 8 under thecondition of a current density of 2 ASD, and tin or tin alloy platingdeposition layers were formed in vias. It was heated to 280° C. using areflow apparatus, the plating deposition layer was dissolved, and a bumpwas formed.

“Via filling properties of the tin or tin alloy plating deposition layerin the via” and “appearance of the tin or tin alloy plating depositionlayer in the via” which will be described later are measured regardingthe plating deposition layer before the reflow, and “dispersion in bumpheight” and “ease of generation of empty spaces” are measured regardingthe bump formed after the reflow of the plating deposition layer. Theresults thereof are shown in Table 6.

(1) Via Filling Properties of Tin or Tin Alloy Plating Deposition Layerin Via

The tin or tin alloy plating deposition layer in the via was observedwith a laser microscope, and a difference in height between the highestpoint and the lowest point of the plating deposition layer was measured.A case where the difference in height exceeded 5 μm was determined as“poor”, a case where the difference in height was 5 μm or less wasdetermined as “excellent”, and these were shown in the column of “viafilling properties” of Table 6.

(2) Appearance of Deposition Layer of Tin or Tin Alloy Plating in Via

The tin or tin alloy plating deposition layer in the via was observedwith a laser microscope, and a surface roughness Ra was measured. A casewhere the surface roughness Ra of the plating deposition layer exceeded2 μm was determined as “poor”, a case where the surface roughness Ra was2 μm or less was judged as “excellent”, and these were shown in thecolumn of “appearance of plating deposition layer” of Table 6.

(3) Dispersion in Bump Height

The height of the bump on the substrate was measured using an automaticappearance inspection device. A height deviation 6 (standard deviation)was calculated from the measured bump heights. A case where the heightdeviation 6 is 3 or less was determined as “uniform”, and a case wherethe height deviation 6 exceeded 3 was determined as “non-uniform”, andthe result thereof were shown in the column of “bump height deviation a”of Table 6.

(4) Ease of Generation of Empty Spaces

Transmission X-ray images were captured for bumps (2,000 in total)arranged at pitch intervals of 180 μm, 250 μm, and 360 μm and havingdiameters of 70 μm, 90 μm, and 120 μm. The captured image was visuallyobserved. A case where one or more empty spaces having a size of 1% ormore with respect to the size of the bump was observed was determined as“NG”, a case where no empty spaces were observed was determined as “OK”,and the results thereof were shown in the column of “ease of generationof empty spaces” of Table 6.

TABLE 6 Evaluation Surfactant Appearance Ease of Mass average Metal ofplating Bump generation Compound molecular other Via filling depositionheight of empty No. weight than Sn properties layer deviation σ spacesExample 1 C-1 1300 — Excellent Excellent 1.8 OK Example 2 C-2 1400 —Excellent Excellent 1.7 OK Example 3 C-3 1100 — Excellent Excellent 1.7OK Example 4 C-4 1200 Ag Excellent Excellent 1.9 OK Example 5 C-5 1300 —Excellent Excellent 1.9 OK Example 6 C-6 2300 Cu Excellent Excellent 2.0OK Example 7 C-7 2200 — Excellent Excellent 1.4 OK Example 8 C-8 1900 —Excellent Excellent 1.9 OK Example 9 C-9 1700 — Excellent Excellent 2.0OK Example 10 (C-1 ) + 1300 — Excellent Excellent 1.8 OK (C-5)Comparative C-10 1700 Cu Excellent Poor 3.4 NG Example 1 ComparativeC-11 2400 — Excellent Poor 2.8 OK Example 2 Comparative C-12 1400 — PoorPoor 3.6 NG Example 3 Comparative C-13 1600 Ag Poor Poor 5.2 NG Example4 Comparative C-14 2300 — Poor Poor 4.9 OK Example 5 Comparative C-152300 — Poor Poor 4.3 NG Example 6 Comparative C-16  800 — Poor Poor 1.5NG Example 7 Comparative C-17 4300 Ag Poor Poor 8.0 NG Example 8

As clearly shown in Table 6, in Comparative Example 1 in which thecompound No. C-10 was used as the surfactant, the p/q in General Formula(1) was excessively small as 0.07. Accordingly, although via fillingproperties were excellent, the appearance of the plating depositionlayer was poor, the bump height deviation 6 was great as 3.4, and theease of generation of empty spaces was NG due to the observation ofempty spaces in the bump. In addition, in Comparative Example 2 in whichthe compound No. C-11 was used as the surfactant, the p/q in GeneralFormula (3) was excessively great as 1.92. Accordingly, although viafilling properties were excellent and the ease of generation of emptyspaces was OK due to no empty spaces observed in the bump, theappearance of the plating deposition layer was poor and the bump heightdeviation 6 was great as 2.8. In contrast, in Examples 1 to 9 in whichthe compounds No. C-1 to C-9 were used as the surfactant, the p/q inGeneral Formulae (1) to (4) was within an appropriate range of 0.10 to1.56 (0.1 to 1.6). Accordingly, the via filling properties and theappearance of the plating deposition layer were both excellent, the bumpheight deviation 6 was small as 1.4 to 2.0, and ease of generation ofempty spaces was OK due to no empty spaces observed in the bump.

Meanwhile, in Comparative Example 3 in which the compound No. C-12 wasused as the surfactant, a in General Formula (1) was excessively largeas 21. Accordingly, the via filling properties and the appearance of theplating deposition layer were poor, the bump height deviation 6 wasgreat as 3.6, and the ease of generation of empty spaces was NG due tothe observation of empty spaces in the bump. In addition, in ComparativeExample 4 in which the compound No. C-13 was used as the surfactant, ain General Formula (1) was excessively small as 10. Accordingly, the viafilling properties and the appearance of the plating deposition layerwere poor, the bump height deviation σ was great as 5.2, and the ease ofgeneration of empty spaces was NG due to the observation of empty spacesin the bump. In contrast, in Examples 1 to 9 in which the compounds No.C-1 to C-9 were used as the surfactant, a in General Formulae (1) to (4)was within an appropriate range of 12 to 18 (12 to 18). Accordingly, thevia filling properties and the appearance of the plating depositionlayer were both excellent, the bump height deviation 6 was small as 1.4to 2.0, and ease of generation of empty spaces was OK due to no emptyspaces observed in the bump.

Meanwhile, in Comparative Example 5 in which the compound No. C-14 wasused as the surfactant, the p/q in General Formula (1) was excessivelylarge as 1.92 and a was excessively small as 9. Accordingly, althoughthe ease of generation of empty spaces was OK due to no empty spacesobserved in the bump, the via filling properties and the appearance ofthe plating deposition layer were poor and the bump height deviation σwas great as 4.9. In contrast, in Examples 1 to 9 in which the compoundsNo. C-1 to C-9 were used as the surfactant, the p/q in General Formulae(1) to (4) was within an appropriate range of 0.10 to 1.56 (0.1 to 1.6)and a was within an appropriate range of 12 to 18 (12 to 18).Accordingly, the via filling properties and the appearance of theplating deposition layer were both excellent, the bump height deviationσ was small as 1.4 to 2.0, and ease of generation of empty spaces was OKdue to no empty spaces observed in the bump.

Meanwhile, in Comparative Example 6 in which the compound No. C-15 wasused as the surfactant, (p+q) was excessively large as 22. Accordingly,the via filling properties and the appearance of the plating depositionlayer were poor, the ease of generation of empty spaces was NG due tothe observation of empty spaces in the bump, and the bump heightdeviation 6 was great as 4.3. In contrast, in Examples 1 to 9 in whichthe compounds No. C-1 to C-9 were used as the surfactant, the p inGeneral Formulae (1) to (4) was within an appropriate range of 1 to 8 (1or more) and (p+q) was within an appropriate range of 8 to 21 (8 to 21).Accordingly, the via filling properties and the appearance of theplating deposition layer were both excellent, the bump height deviation6 was small as 1.4 to 2.0, and ease of generation of empty spaces was OKdue to no empty spaces observed in the bump.

Meanwhile, in Comparative Example 7 in which the compound No. C-16 wasused as the surfactant, p in General Formula (1) was excessively smallas 0 and (p+q) was excessively small as 5. Accordingly, although thebump height deviation 6 was small as 1.5, the via filling properties andthe appearance of the plating deposition layer were poor and the ease ofgeneration of empty spaces was NG due to the observation of empty spacesin the bump. In contrast, in Examples 1 to 9 in which the compounds No.C-1 to C-9 were used as the surfactant, the p in General Formulae (1) to(4) was within an appropriate range of 1 to 8 (1 or more) and (p+q) waswithin an appropriate range of 8 to 21 (8 to 21). Accordingly, the viafilling properties and the appearance of the plating deposition layerwere both excellent, the bump height deviation 6 was small as 1.4 to2.0, and ease of generation of empty spaces was OK due to no emptyspaces observed in the bump.

In Comparative Example 8, polyoxyethylenepolyoxypropylene-ethylenediamine of the compound No. C-17 was used asthe surfactant. Accordingly, the via filling properties and theappearance of the plating deposition layer were poor, the bump heightdeviation σ was large as 8.0, and the ease of generation of empty spaceswas NG due to the observation of empty spaces in the bump. In Example10, a mixture obtained by mixing the compound No. C-1, to which GeneralFormula (1) was applied, and the compound No. C-5, to which GeneralFormula (2) was applied, was used as the surfactant, but the via fillingproperties and the appearance of the plating deposition layer were bothexcellent, the bump height deviation 6 was small as 1.8, and ease ofgeneration of empty spaces was OK due to no empty spaces observed in thebump.

Examples 11 to 20

In Examples 11 to 20, a Sn plating solution was prepared in the samemanner as in Example 1, except that any of the first leveling agent(D-1), the second leveling agent (D-2), or the metal other than Sn, andthe mass average molecular weight of the surfactant were changed asshown in Table 7. In the first leveling agent (D-1) of Table 7, D1A isbenzaldehyde, D1B is 4-chlorobenzaldehyde, and D1C is 1-naphthaldehyde.In addition, in the second leveling agent (D-2) of Table 7, D2A ismethacrylic acid, D2B is acrylic acid, and D2C is acrylamide.

Comparative Test 2 and Evaluation

The plating was performed on a substrate having a pattern havingdifferent bump diameters using the 10 types of the prepared platingsolutions of Examples 11 to 20 under the condition of a current densityof 2ASD in the same manner as in the comparative test 1, and tin or tinalloy plating deposition layers were formed in vias. It was heated to280° C. using a reflow apparatus, the plating deposition layer wasdissolved to form a bump, and the “via filling properties of the tin ortin alloy plating deposition layer in the via”, the “appearance of thetin or tin alloy plating deposition layer in the via”, the “dispersionin bump height”, and “ease of generation of empty spaces” wereevaluated. Table 7 shows the results thereof.

TABLE 7 First leveling Second leveling agent Surfactant Evaluation agent(D-1) (D-2) Mass Appearance Ease of Concen- Concen- Com- average Metalof plating Bump generation tration tration pound molecular other Viafilling deposition height of empty Type (g/L) Type (g/L) No. weight thanSn properties layer deviation σ spaces Example 11 D1A 0.1 D2A 2 C-3 1300— Excellent Excellent 1.9 OK Example 12 D1B 0.1 D2A 2 C-3 1300 —Excellent Excellent 2.3 OK Example 13 D1C 0.1 D2B 2 C-3 1300 — ExcellentExcellent 2.0 OK Example 14 D1C 0.1 D2C 2 C-3 1300 — Excellent Excellent2.1 OK Example 15 D1A 0.1 D2A 2 C-3 1300 Cu Excellent Excellent 1.8 OKExample 16 D1C 0.1 D2C 2 C-3 1300 Ag Excellent Excellent 1.8 OK Example17 D1C 0.001 D2A 2 C-3 1300 — Excellent Excellent 1.7 OK Example 18 D1C0.3 D2A 2 C-3 1300 — Excellent Excellent 2.4 OK Example 19 D1C 0.1 D2A0.05 C-3 1300 — Excellent Excellent 2.2 OK Example 20 D1C 0.1 D2A 30 C-31300 — Excellent Excellent 1.7 OK

As clearly shown from Table 7, in Examples 11 to 14 in which the firstleveling agent (D-1) was changed to any of benzaldehyde,4-chlorobenzaldehyde, or 1-naphthaldehyde, and the second leveling agent(D-2) was changed to any of methacrylic acid or acrylic acid, the viafilling properties and the appearance of the plating deposition layerwere both excellent, the bump height deviation a was uniform as 1.9 to2.3, and ease of generation of empty spaces was OK due to no emptyspaces observed in the bump.

In addition, in Examples 15 and 16 in which the first leveling agent(D-1) was changed to benzaldehyde or 1-naphthaldehyde, the secondleveling agent (D-2) was changed to methacrylic acid or acrylamide, andCu or Ag was added as the metal other than Sn, the via fillingproperties and the appearance of the plating deposition layer were bothexcellent, the bump height deviation a was uniform as 1.8, and ease ofgeneration of empty spaces was OK due to no empty spaces observed in thebump.

Further, in Examples 17 and 18 in which the concentration of the firstleveling agent (D-1) was changed to 0.001 g/L and 0.3 g/L, respectively,and in Examples 19 and 20 in which the concentration of the secondleveling agent (D-2) was changed to 0.05 g/L and 30 g/L, respectively,the via filling properties and the appearance of the plating depositionlayer were both excellent, the bump height deviation a was uniform as1.7 to 2.4, and ease of generation of empty spaces was OK due to noempty spaces observed in the bump.

INDUSTRIAL APPLICABILITY

The tin or tin alloy plating solution of the invention can be used for acircuit board such as a printed circuit board, a flexible printedcircuit board, and a semiconductor integrated circuit.

REFERENCE SIGNS LIST

1: Substrate

2: Solder resist layer

3: Copper seed layer

4: Dry film resist layer

6: Via

7: Tin plating deposition layer (tin plating film)

8: Tin bump

The invention claimed is:
 1. A method of forming a tin or tin alloy deposition layer comprising the step of forming a tin or tin alloy deposition layer on a substrate with vias having different via diameters by using a tin or tin alloy plating solution, wherein the tin or tin alloy plaiting solution comprises: (A) a soluble salt containing at least a stannous salt; (B) an acid selected from an organic acid and an inorganic acid or a salt thereof; (C) a surfactant; and (D) a leveling agent, wherein the surfactant contains polyoxyethylene polyoxypropylene alkylamine selected from the group consisting of general formulae (1), (3) and (4):

wherein R¹ represents C_(a)H_(2a−1), a is an integer from 12 to 18, p and q are each 1 or more, a sum of p and q is an integer from 8 to 21, and a ratio of p to q, p/q, is 0.1 to 1.6, the leveling agent is made of a first leveling agent and a second leveling agent, the first leveling agent is one or more selected from a group consisting of aliphatic aldehyde, aromatic aldehyde, aliphatic ketone and aromatic ketone, and the second leveling agent is α,β-unsaturated carboxylic acid or α,β-unsaturated carboxylic acid amide, or a salt thereof.
 2. The method of forming a tin or tin alloy plating deposition layer according to claim 1, wherein the tin or tin alloy plating solution further comprises two or more of: a surfactant other than the surfactant; an antioxidant; and an alcohol having 1 to 3 carbon atoms.
 3. A method for forming a bump comprising the step of performing a reflow process on the tin or tin alloy plating deposition layer formed by the method of forming a tin or tin alloy deposition layer according to claim
 1. 4. A method for producing a circuit board using the bump formed by the method according to claim
 3. 5. A method for forming a bump performing a reflow process comprising the step of performing a reflow process on the tin or tin alloy plating deposition layer formed by the method of forming a tin or tin alloy deposition layer according to claim
 2. 6. A method for producing a circuit board using the bump formed by the method according to claim
 5. 7. The method of forming a tin or tin alloy deposition layer according to claim 1, wherein the tin or tin alloy deposition layer is formed by electroplating under a single current density.
 8. The method of forming a tin or tin alloy deposition layer according to claim 1, wherein the polyoxyethylene polyoxypropylene alkylamine is selected from the group consisting of general formulae (1) and (3). 